Basic Sciences Relevant to Psychiatry
Core concepts
Know the dopamine pathways and their clinical correlates: mesolimbic (positive symptoms), mesocortical (negative/cognitive symptoms), nigrostriatal (extrapyramidal effects), tuberoinfundibular (prolactin regulation). Map receptors to side effects: H1 (sedation, weight gain), muscarinic M1 (anticholinergic effects, cognitive blunting), alpha-1 (orthostasis, reflex tachycardia), D2 (EPS, hyperprolactinemia). Understand serotonin anatomy (raphe nuclei), noradrenergic locus coeruleus, and the HPA axis with dexamethasone suppression. Learn the cytochrome P450 system - 1A2 (clozapine, olanzapine; inhibited by fluvoxamine, induced by smoking), 2D6 (many antidepressants and antipsychotics; genetic polymorphism), 3A4 (carbamazepine, quetiapine). Know the mechanism families: SSRIs, SNRIs, TCAs (sodium-channel cardiotoxicity), MAOIs (tyramine/cheese reaction, serotonin syndrome), mood stabilizers (lithium's second-messenger and inositol effects; valproate's GABAergic action). Genetics: heritability estimates, twin and adoption designs, and concepts like anticipation and imprinting.
Traps
Questions often conflate mechanism with side effect (e.g., asking which receptor mediates weight gain - H1, not D2). Distinguish serotonin syndrome (clonus, hyperreflexia, autonomic instability) from neuroleptic malignant syndrome (rigidity, hyperthermia, raised CK, lead-pipe). Watch for lithium toxicity triggers (dehydration, NSAIDs, thiazides, ACE inhibitors) and the timing of therapeutic drug monitoring (12 hours post-dose).
Rule of thumb
When asked about an interaction, identify the enzyme and whether the drug is a substrate, inhibitor, or inducer - inhibitors raise levels, inducers lower them.